Electrochromic rearview mirrors have long been incorporated into vehicles for providing automatic control of glare (variable transmission) to a vehicle operator. EC rearview mirrors are often times mounted both inside and outside the vehicle or only on the inside. Some of the patents that describe electrochromic devices usable for mirrors are U.S. Pat. Nos. 3,280,701; 4,712,879; 4,902,108; 5,140,455; 5,724,187; 6,111,684; 6,166,848; 6,853,472 and published patent application 2004/0233537. Many aspects of this invention may be used for other type of electrooptic devices (e.g., liquid crystal, suspended particle devices, user controllable photochromic devices, photo-electrochromic devices) that result in variable transmission/reflective devices for use in windows and automotive mirrors. All of these devices including EC devices are called chromogenic devices. Chromogenic devices also include photo-electrochromic or user controllable photochromic devices. The innovation disclosed here is applicable to all of these chromogenic devices that are used as variable reflectance automotive mirrors and variable transmission windows for architectural and transportation use (windows for cars, busses, airplanes, boats, etc.). The claims of this innovation exclude displays and applications related to displays.
Commercially available mirror assemblies comprise of an EC cell enclosed in a casing along with an attachment mechanism to the vehicle, powering electronics and other electrical and electronic features. These mirror assemblies may comprise of materials which are harmful to the environment. In one aspect, this invention describes novel combination of materials to reduce environmental degradation and safety, particularly for those who are involved when these systems are being made, removed, recycled or disposed at the end of their life cycle. In another aspect, the materials of this invention assist in reducing the assembly of the chromogenic cell, by reducing the material and the processing cost. Yet another aspect of this innovation is that it allows forming objects with higher performance characteristics. One of the areas where this invention focuses on are conductive busbars, both materials and processes, so that these can be made without beryllium. In addition, this invention also addresses improved perimeter sealants to enhance the device reliability. Such busbars and sealants may be used for other chromogenic rearview mirrors and window devices. These window devices may be used for architectural applications, transportation windows for vehicle use and other transportation medium (planes, trains, buses and boats). These windows may be used as optical filters, but are not used as displays.
Most EC mirrors for vehicles in the market use a construction as shown in FIG. 1a. This prior art is shown schematically as a device cross-section, where an EC mirror is constructed using two substrates 10 and 20. 21 is a transparent conductor and 11 is a layer or a layer stack which is both electrical conductor and a reflector. This is assembled into a cavity using a perimeter adhesive 15 where the cavity thickness is determined by spacers in the adhesive and/or sprinkled throughout the cavity (not shown). The interior of the cavity has an electrochromic medium 23 which may comprise of one or more layers. The electrochromic medium may be substituted by a liquid crystalline formulation or a suspended particle formulation. For electrical connections busbar clips are attached to both substrates as 17 and 18 which are then connected to powering wires 13 and 14 respectively. The busbar clips in commercial mirrors are generally made of copper-beryllium alloy as described earlier; however, beryllium free busbars are preferred for environmental reasons. In some cases one may substitute clips by conductive adhesives being used in these applications as busbars and connectors. Most conventional conductive adhesives use large sized silver particles (typically in microns) in an organic matrix (e.g., epoxy). These silver particles have flake like geometry with a tap density in the range of 2 to 4 g/cm3 (bulk density of silver is 10.5 g/cm3) and surface area in the range of 0.5 to 2 m2/g) based on this one can calculate the average thickness of the flakes (calculated using a formula, where thickness=1/(surface area*bulk density)) which comes out in the range of 0.48 to 2 μm assuming no porosity. The thickness numbers will be higher if there is porosity. A general description of silver flakes for conventional conductive adhesives is provided in Sica, M. 2008. However, with the quantity of the silver required and the high silver prices such adhesives are expensive. Materials that result in busbars with higher conductivity (even if silver particles are used), will be preferred, so that silver use can be reduced, and better performance can be obtained. The electrical connections and the adhesive line is concealed from the user by an opaque bezel 16, generally made out of a colored plastic material (usually polypropylene, polyurethane or acrylonitrile-butadiene-styrene terpolymer). Improved perimeter sealants with a two phase structure in the resin, which result in more reliable bonding, are also disclosed.
FIG. 1a, shows a third surface mirror. The surfaces on the substrate are counted from the side the mirror is viewed, where the first surface is outside surface of the first substrate, the second surface is the inner surface of the second substrate, the third surface is the inner surface of the second surface and the fourth surface is the outside surface of the second substrate. The third surface reflective layer may comprise of several coats of materials both transparent conductors and reflective layers. More on this is discussed in several US patents such as U.S. Pat. Nos. 3,280,701; 5,724,187; 5,818,625 and published US patent application 2004/0233537. When the reflector is on the third surface then the mirrors are called third surface mirrors, and when the reflector is on the fourth surface then they are called fourth surface mirrors. As shown in FIG. 1a, the mirror cell is assembled using two substrates (20 and 10) coated with conductive coatings (21 and 11 respectively), and these are bonded using a perimeter sealant 15. During their manufacture a small hole is left in the sealant through which the electrolyte 23 is introduced in the chamber formed by the two substrates. Typically the perimeter sealant has spacer beads which result in a controlled chamber thickness. After filling the chamber (also called cavity) the hole is generally sealed with a UV curing sealant (also called plug sealant). Clips 17 and 18 are generally used to connect the conductive coatings on the substrates using wires 13 and 14 to the rest of the electronics. This mirror is enclosed in a case and 16 shows the front bezel of the case (one may also make without bezels as discussed in US patent application 2008/0074724). In the mirror housing (behind the mirror one has electronics) to power the mirror and provide any other features. The EC devices (including mirrors from other chromogenic devices), may also be filled by the injection of the electrolyte. Typically in the injection process two ports are required in the cavity, one for filling and other to evacuate the gas in the cavity as the fill proceeds. This is described in published US patent application 20090095408 which is enclosed herein by reference. FIG. 1b shows the schematics of a complete EC mirror assembly. The EC mirror is powered and controlled by a controller which may be in the same housing as the mirror (which is generally the case) or external to it. The controller may have integrated chips which preferably should not use any components utilizing beryllium or beryllium oxide. The controller is supplied by power from the car power system or one may use a secondary (rechargeable) or a primary battery. It also receives two light intensity signals, one for glare level (typically a light transducer or sensor facing towards the rear of the car) and the other for ambient light (which is typically facing towards the front of the car), so that it can compare and decide if the glare is being caused at night by a vehicle trailing the car with the system. The controller may have other inputs such as if the car is in reverse gear or not (so that the EC mirror darkening may be disabled automatically when reversing), inputs for other added features such as for temperature, cameras for video displays, micro-phone and speaker for phone system, and may have added features such as compass, rain sensor, garage door openers, headlight control amongst many others. Many of these features are described in several patents and patent applications. Some of these are US patent application 2007/0,285,789; and U.S. Pat. No. 7,087,878. The controller (or electronics module) can be on a flexible substrate or this may be mounted behind the mirror (back side of the rear substrate). These descriptions and also where the mirror casing itself may be used as a substrate to connect electronic components is disclosed in U.S. provisional patent applications, Ser. No. 61/431,567, filed on Jan. 11, 2011, and Ser. No. 61/481,172 filed on Apr. 30, 2011 which are enclosed herein by reference. Busbars for these disclosures can gain from this innovation where these busbars can be deposited by a printing process or a spray process (e.g., Aerosol Jet technology from Optomec Inc. Albuquerque, N. Mex.), as discussed later.
Most commercial EC automotive mirrors use liquid or solid electrolytes, which when disposed have the potential to contaminate. To minimize disposal volume, it is preferred to reduce the quantity of electrolyte in these mirrors. The electrolytes typically comprise of electrochromic dyes, UV stabilizers, electrolytic salts, monomers, initiators, and polymers.
devices are made in many different layer configurations. EC devices shown in FIG. 1a (where no reflector layer is used, and both 21 and 11 are transparent conductors) are used in commercial air-craft EC windows. In many of the architectural windows, layer configurations as shown in FIGS. 1c and 1d are used, as this reduces the back reaction. In FIG. 1c the EC device is constructed on a single substrate 10c, where 11c and 21c are transparent conductors. Layer 23c is the electrolyte (or ion conductor), and layers 24c and 25c are one of each of electrochromic layer and the counter electrode. The counterelectrode may also have electrochromic properties. As seen the electrochromic medium of this construction is sandwiched between two conductive layers 11c and 21c, which are both transparent for a window, and if one of them has reflective properties then it becomes a mirror. Also shown in this figure is a deletion line 26c which breaks the continuity of the conduction path between the two sections of the transparent conductor 11c. This deletion line may be etched using lasers or by chemical etching, or this is an area that is masked off, if the process to deposit the transparent conductor can be customized. Since the transparent conductor 21c, touches a section of 11c, this device can be powered by applying a voltage across the deletion line (which then applies a voltage across the layer stack. The busbar 27c will typically run along the side of the device or more of the perimeter depending on the conductivity of the layer 21c. Similarly, busbar 28c will be used to power the other side. As discussed later, the busbar electrical resistance is smaller than the electrical resistance of the transparent conductor it is deposited on. The reason is that the busbar may make a point contact (or at several points if the busbar is too long, so that the resistance between the points is less than about 5Ω, (preferably less than or equal to 1Ω, and most preferably less than or equal to 0.5Ω) with the electrical wire to power the device, and the voltage drop across the busbar length needs to be minimized so that the voltage can be effectively distributed evenly over most of the perimeter of the EC device. There are many variations in these devices, e.g., where each of the layers described may be composed of multiple layers with different compositions. Such devices for EC architectural windows are described in the literature, and some exemplary references are published US patent applications 20090285978, 20100007937, 20080304130.
FIG. 1d shows another type of EC device, which like FIG. 1a comprises of two substrates 10d and 20d. For windows, each of the substrates has a transparent conductive layer 11d and 21d. Layer 11d has an additional electrochromic layer 24d deposited on it and the layer 21d has an additional counterelectrode layer 25d deposited on it. The counterelectrode may also have electrochromic properties. These are then laminated together so that the lamination layer is the ion conductive or the electrolyte layer 23d. The device is sealed at the perimeter using an adhesive 29d. Further, busbars 27d and 28d are deposited along the length of the device (or even one length and one width or even the entire perimeter (as long as these do not touch). In this construction also the electrochromic medium is sandwiched between two conductive layers. An example of this kind of device is in published US patent application 20090225393 (and also see Jödicke, D., Wittkopf, H., The 2nd generation of an electrochromic solar control glazing—ready for projects, Proceedings-Glass performance Days (2007) p-394-395).
There are other electrochromic devices with different layer configurations (see U.S. Pat. No. 6,178,034). There is another type of related device that make use of the electrochromic layer in an interesting way. These are called photo-electrochromic or user controllable photochromic devices (e.g., see U.S. Pat. No. 5,838,483 and U.S. Pat. No. 7,855,822), which also use an electrochromic medium between two conductors, wherein these conductors are transparent for use as a window. These also use busbars at the perimeter to be able to connect to electric cables so that these can be electronically controlled. The busbars described in this invention being disclosed are applicable to all of these devices. Perimeter busbars may be deposited around the entire perimeter, or part of the perimeter. Busbars for many type of chromogenic devices are described in U.S. Pat. No. 6,317,248, which is included herein by reference. This patent also discusses the use of internal busbars, which are passivated so that these do not react with the layers that are deposited on them or with the ions when the EC devices are powered. In addition, transparent conductor compositions and multilayer transparent conductor compositions that are novel to EC devices are also disclosed.